Updated mnist example README with AWS credentials setting

mnist/README.md

@@ -354,20 +354,20 @@ various environment variables configuring access to S3.
        --from-literal=awsSecretAccessKey=${AWS_SECRET_ACCESS_KEY}
      ```
   
-  1. Mount the secret into the pod
+  1. Pass secrets as environment variables into pod
 
      ```
-     ks param set --env=${KSENV} train secret aws-creds=/var/secrets
+     ks param set --env=${KSENV} train secretKeyRefs AWS_ACCESS_KEY_ID=aws-creds.awsAccessKeyID,AWS_SECRET_ACCESS_KEY=aws-creds.awsSecretAccessKey
      ```
 
-     * Setting this ksonnet parameter causes a volumeMount and volume to be added to your TFJob
+     * Setting this ksonnet parameter causes a two new environment variables to be added to your TFJob
      * To see this you can run
 
        ```
        ks show ${KSENV} -c train
        ```
 
-     * The output should now include a volumeMount and volume section
+     * The output should now include two environment variables referencing K8s secret
 
        ```
         apiVersion: kubeflow.org/v1beta1
@@ -384,15 +384,18 @@ spec:
               containers:
               - command:
               ...
-            volumeMounts:
+                env:
-            - mountPath: /var/secrets
-              name: aws-creds
-              readOnly: true
                 ...
-          volumes:
+                - name: AWS_ACCESS_KEY_ID
-          - name: aws-creds
+                  valueFrom:
-            secret:
+                    secretKeyRef:
-              secretName: aws-creds
+                      key: awsAccessKeyID
+                      name: aws-creds
+                - name: AWS_SECRET_ACCESS_KEY
+                  valueFrom:
+                    secretKeyRef:
+                      key: awsSecretAccessKey
+                      name: aws-creds
                       ...
       ```